Various types of implantable interbody devices, which also may be referred to as “spacers” or “cages,” are commonly used in spinal fusion surgery to restore and maintain normal spacing between adjacent vertebrae. In particular, one or more interbody devices may be inserted into the intervertebral space, which also may be referred to as the “interbody space” or the “disc space,” between two adjacent vertebrae to provide structural support and stabilization of the vertebrae. In addition to expanding the intervertebral space to its normal spacing or “height,” interbody devices may realign the adjacent vertebrae such that the vertebrae follow the normal curvature of the spine. For example, in the lumbar region of the spine, interbody devices may provide correction of lordosis, the normal inward curvature of the lumbar region. Interbody devices may be used in the treatment of various spinal conditions, including spondylolisthesis, degenerative disc disease, and recurrent disc herniation. In many applications, interbody devices may be used in conjunction with additional hardware, such as pedicle screws and rods or plates, which provide additional structural support to stabilize the desired vertebrae and facilitate fusion therebetween.
In the lumbar region of the spine, interbody fusion (i.e., solid bone growth formed within the intervertebral space and connecting the adjacent vertebrae) may be achieved by a number of techniques, including posterior lumbar interbody fusion (PLIF), transforaminal lumbar interbody fusion (TLIF), extreme lateral interbody fusion (XLIF), and anterior lumbar interbody fusion (ALIF). The PLIF and TLIF techniques utilize a posterior approach, which generally requires removal of portions of the adjacent vertebrae in order to access the desired intervertebral space and allow for insertion of an interbody device therein. For example, complete or partial removal of the laminae and/or the facet joints may be required to provide a sufficient access window for subsequent removal of intervertebral disc material and insertion of the interbody device. The size of the access window necessary may be driven largely by the size of the interbody device being implanted. In some instances, distraction of the intervertebral space, via one or more instruments, may be required to allow for insertion of the interbody device therein. In other instances, the interbody device itself may distract the intervertebral space as the device is inserted therein. Upon insertion and positioning of the interbody device within the intervertebral space, the device may restore the normal spacing between the adjacent vertebrae and provide lordosis correction. According to the PLIF technique, two interbody devices generally are implanted, one in the left side of the intervertebral space and another in the right side of the intervertebral space. In contrast, the TLIF technique generally utilizes a single interbody device implanted in the middle of the intervertebral space via the right or left side of the spine.
In order to promote fusion between the adjacent vertebrae, bone graft (either autograft or allograft) or a bone graft substitute is commonly inserted into the intervertebral space. In some instances, the bone graft may be placed within one or more cavities of the interbody device, either before or after the device is inserted into the intervertebral space. Additionally or alternatively, the bone graft may be placed alongside the interbody device. Ultimately, the interbody device, itself or in combination with additional hardware, may provide the structural support necessary to maintain the normal spacing and alignment of the adjacent vertebrae until fusion is achieved between the vertebrae.
Various interbody devices and related instruments and methods have been developed for use in spinal fusion surgery. However, existing devices, instruments, and methods may suffer from several potential drawbacks. For example, certain existing interbody devices may be difficult to insert and position within the intervertebral space and/or may require significant distraction of the intervertebral space via separate instruments to allow for insertion and desired positioning. In particular, some interbody devices designed for insertion via a posterior approach and configured to provide lordosis correction may be challenging to insert and position within the intervertebral space without significant distraction via separate instruments, which may complicate the implantation procedure. Additionally, certain existing interbody devices may require a relatively large access window (created by removal of portions of the adjacent vertebrae) to allow for insertion of the device into the intervertebral space. In particular, some interbody devices designed for insertion via a posterior approach may have a relatively large insertion profile that necessitates complete or substantial removal of the laminae and/or the facet joints, which may complicate the implantation procedure, compromise the structural integrity of the affected vertebrae, and extend the post-operative healing process. According to certain designs, a large insertion profile may be driven by a large footprint of the interbody device in the transverse plane of the patient, which also may be referred to as the “axial” plane, as may be selected to provide desired structural support between the adjacent vertebrae.
Certain existing interbody devices may be configured for vertical expansion (i.e., expansion in the sagittal plane and/or the coronal plane of the patient) within the intervertebral space to restore normal spacing and alignment of the adjacent vertebrae, or may be configured for lateral expansion (i.e., expansion in the transverse plane of the patient) within the intervertebral space to provide an enlarged footprint for enhancing structural support of the vertebrae. Such expandable devices may have complicated designs including numerous parts that are susceptible to malfunction or failure during or after implantation of the device. Moreover, expandable interbody devices may include complex expansion mechanisms or may require the use of complex expansion instruments, which may complicate the implantation procedure and may lead to high manufacturing costs of the device and the instrument. Some laterally-expandable interbody devices may be configured to expand to a predetermined degree of expansion, lacking a means for controllably expanding the device to a user-determined degree of expansion as may be desired to accommodate a patient's anatomy. Additionally, some laterally-expandable interbody devices may not adequately support the adjacent vertebrae in the anterior and posterior regions of the intervertebral space in a manner that provides desired lordosis correction.
As described above, certain interbody devices may include one or more cavities configured to receive and contain bone graft or a bone graft substitute therein. However, the cavities of certain existing interbody devices, particularly non-expandable devices, may be relatively small, limiting the amount of bone graft that may be placed and contained therein and often necessitating placement of additional bone graft alongside the device, which may be susceptible to undesirable migration within and out of the intervertebral space. Certain expandable interbody devices may provide larger cavities for receiving bone graft, as compared to non-expandable devices. However, bone graft placed in the cavity of expandable interbody devices may be susceptible to undesirable migration out of the cavity and potentially out of the intervertebral space (such as posteriorly into the neural foramen or the spinal cord). Such migration may be of particular concern with expandable interbody devices that provide a cavity that is largely open in the posterior direction, especially when the device was inserted into the intervertebral space through and access window formed in the posterior of the spine.
A need therefore exists for improved interbody devices and related instruments and methods that address one or more of the above-described potential drawbacks of existing devices, instruments, and methods for spinal fusion surgery.